OPA: Fail fast on discovery or bundle download errors

[mjungsbluth]

As part of #3119, this PR changes the behaviour on starting up OPA instances inside the OPA based Skipper filters.

Currently even in the face of download errors of bundles, the default timeout of 30s is applied.

By using listeners both for bundle download and discovery bundle download, we can detect a failure early despite the respective plugins still waiting for the bundles to become available.

Still a draft because tests are missing, there are some cleanups in the code that need to be done.

Pending: Unregister discovery and bundle plugin listeners.